1. Technical Field
The present invention relates to a variable nozzle unit capable of varying a passage area for (a flow rate of) an exhaust gas supplied to a turbine impeller side of a variable geometry system turbocharger, and the like.
2. Description of the Related Art
Various developments have been made for variable nozzle units to be installed in variable geometry system turbochargers in recent years.
A concrete configuration of a variable nozzle unit according to a conventional technology is as follows. Inside a turbine housing of a variable geometry system turbocharger, a base ring is disposed concentrically with a turbine impeller. Multiple supporting holes are formed to penetrate the base ring at equal intervals in the circumferential direction of the base ring. Furthermore, multiple variable nozzles are disposed on the base ring at equal intervals in the circumferential direction in such a way as to surround the turbine impeller. The variable nozzles are rotatable about their respective axes which are parallel to the axis of the turbine impeller. Moreover, a nozzle shaft is integrally formed on a side surface of each variable nozzle on one side in the axial direction of the turbine impeller. Each nozzle shaft penetrates and is rotatably supported by its corresponding supporting hole in the base ring.
A link mechanism for synchronously rotating the multiple variable nozzles is disposed on one side of the base ring in the axial direction.
A concrete configuration of the link mechanism is as follows. On the one side of the base ring in the axial direction, a driving ring is provided rotatably and concentrically with the base ring. In addition, as many synchronous joint members as the variable nozzles are disposed on the driving ring at equal intervals in the circumferential direction. Each synchronous joint member has power transmission surfaces on two sides in the circumferential direction (on two sides in a direction orthogonal to the radial direction). Furthermore, a driving joint member is provided to the driving ring. The driving joint member has power transmission surfaces on two sides in the circumferential direction.
A base end portion of a nozzle link member is integrally connected to the nozzle shaft of each variable nozzle. A tip end side of each nozzle link member is engaged with its corresponding synchronous joint member in such a way as to sandwich the synchronous joint member from the two sides. In addition, each nozzle link member has a pair of power transmission surfaces on its tip end side, which can be brought into sliding contact with the power transmission surfaces of the corresponding synchronous joint member.
A driving shaft is provided in a bearing housing as a fixed section of the variable geometry system turbocharger in such a way as to be rotatable about its axis parallel to the axis of the turbine impeller. The driving shaft is rotated by the drive of a rotary actuator. A base end portion of a driving link member is integrally connected to an end portion of the driving shaft on an opposite side in the axial direction. A tip end side of the driving link member is engaged with the driving joint member in such a way to sandwich the driving joint member. Moreover, the driving link member has a pair of power transmission surfaces on its tip end side, which can be brought into sliding contact with the power transmission surfaces of the driving joint member.
Accordingly, if the engine speed is in a high speed range while the variable geometry system turbocharger is in operation, the drive of the rotary actuator rotates the driving shaft in one direction, thus swinging the driving link member in the one direction, and rotating the driving ring in a forward direction. This swings the multiple nozzle link members in the forward direction, and concurrently rotates the multiple variable nozzles synchronously in the forward direction (opening direction). Thus, it is possible to increase the passage area for (the flow rate of) the exhaust gas to be supplied to the turbine impeller side.
On the other hand, if the engine speed is in a low speed range, the drive of the rotary actuator rotates the driving shaft in the other direction, thus swinging the driving link member in the other direction, and rotating the driving ring in a reverse direction. This swings the multiple nozzle link members in the reverse direction, and concurrently rotates the multiple variable nozzles synchronously in the reverse direction (closing direction). Accordingly, it is possible to decrease the passage area for the exhaust gas to be supplied to the turbine impeller side.